A wireless communication device, e.g., a mobile device, may include a real-time clock, e.g., a 32 Kilohertz (kHz) real-time clock, to keep track of time, and to provide a clock signal to one or more elements of the wireless communication device, for example, to communicate with one or more other wireless communication devices, to cause one or more elements of the wireless communication device to “wake up” from a reduced power mode, and/or to perform one or more other operations.
Most real-time clocks have a precision of 100 to 250 parts per million (PPM), which may be adequate to keep a device from seeming unresponsive or “sluggish”.
The wireless communication device may be configured to perform clock synchronization operations and communications to enable communication with another device.
In one example, a Bluetooth device may communicate over a slotted channel according to a Time-Division Duplex (TDD) scheme, e.g., to support full duplex transmission. According to a Bluetooth communication scheme, information is exchanged between devices through frames, each frame being transmitted on a different hop frequency. A frame nominally covers a single slot, but can be extended to cover up to five slots. For a mobile device, even in idle mode, a Bluetooth radio is turned on, and wakes up every few seconds for a period long enough to make sure no paired device is wishing to transfer data.
In another example, in a power save mode (PSM) of a Wireless Local Area Network (WLAN), e.g., according to the IEEE 802.11 standards, time is divided into periods called beacon intervals. A Timing Synchronization Function (TSF) uses beacons to synchronize clocks among stations to ensure that all stations wake up at the same time. A device may be required to perform often scans to detect the beacons.
Even a small clock drift, e.g., a drift of 20 PPM, may require buffer time to make sure that devices are connected properly before data is transferred.
It has been shown that clock synchronization between devices may account for about 50% of a power consumption of some devices, e.g., wearable devices.